Peters et al. in U.S. Pat. No. 2,892,826 describe the polymerization of olefins in the presence of diborane, other hydrides of boron, or lower boron alkyls adsorbed or absorbed on a group 5a oxide.
The use of chromium compounds in the polymerization of olefins is also well-known. U.S. Pat. Nos. 2,825,721 and 2,951,816 teach the use of CrO.sub.3 supported on an inorganic material such as silica, alumina or combinations of silica and alumina, and activated by heating in reducing atmospheres, to polymerize olefins. When, however, a catalyst system of this type is used in techniques such as the well-known particle-form process, the resins produced, while useful in many applications, are unsatisfactory for others because of a deficiency in certain properties such as melt index.
Attempts to improve the properties of polyolefins produced using supported, heat-activated chromium oxide catalysts have been made by adding various compounds to the supported chromium oxide prior to the heat activation thereof. Thus, U.S. Pat. No. 3,484,428 discloses adding boranes or alkyl-substituted boranes to such a catalyst, and U.S. Pat. No. 3,780,011 refers to the use of alkyl esters of boron.
It is also known to utilize other chromium compounds as catalysts for the polymerization of olefins. Such compounds include various silyl chromate and polyalicyclic chromate esters as described, for example, in U.S. Pat. Nos. 3,324,095; 3,324,101; 3,642,749; and 3,704,287. The use of phosphorus-containing chromate esters in olefin polymerization catalysts has also been disclosed in the aforesaid U.S. Pat. No. 3,704,287; and in U.S. Pat. Nos. 3,474,080 and 3,985,676. Other such catalysts are described in copending and commonly assigned application Ser. No. 759,213 filed Jan. 13, 1977 and now Pat. No. 4,100,104. Copending and commonly assigned application Ser. No. 693,803, now Pat. No. 4,118,340 of Rekers claims catalysts comprising reaction products of chromium trioxide and an organoborate compound such as triethyl borate.
Certain of these catalytic materials may be employed in Ziegler-type coordination catalyst systems, or in supported form, alone or in conjunction with metallic or organometallic reducing agents such as, for example, trialkyl aluminum compounds or alkyl boranes. Catalyst systems incorporating supported chromium compound catalysts and organometallic reducing agents, particularly organoaluminum compounds, are disclosed, for example, in U.S. Pat. Nos. 3,324,101; 3,642,749; 3,704,287; 3,806,500; 3,985,676; and in the aforesaid copending application Ser. No. 759,213, now Pat. No. 4,100,104.
It has also been disclosed in U.S. Pat. Nos. 3,984,351 and 4,049,896, owned by the assignee of the present invention, that the properties of olefin polymers, e.g., melt indexes, may be substantially improved by the use of a catalyst prepared by depositing chromium and aluminum compounds on an inorganic support material and heat-activating the supported composition in a nonreducing, preferably oxygen-containing atmosphere, at a temperature of from about 300.degree. C. (572.degree. F.) up to the decomposition temperature of the support. The resulting material, as preferably combined with a metallic and/or non-metallic reducing agent, e.g., a trialkyl borane, provides a catalyst system capable of producing polymers having improved flow properties and shear responses in addition to increased melt indexes.
It is among the objects of the present invention to provide yet a further improved technique for preparing catalytic materials, especially olefin polymerization catalysts, and a polymerization process utilizing the same which results in the formation of polymers having increased melt indexes, and improved flow properties, shear response and other desired characteristics.